1. Field of the Invention
The present invention relates to battery packs such as electric vehicle (EV) battery packs in which a casing accommodates a plurality of battery cells.
2. Description of the Related Art
For example, a Japanese patent laid open publication No. JP 2007-329047 has disclosed a battery pack having a conventional structure equipped with a battery pack casing. The battery pack casing accommodates a plurality of battery cell stacks. In each of the battery cell stacks, a plurality of battery cells is stacked in a specific direction. The battery pack casing has an inlet section and an outlet section or a discharge section. Outside air is introduced into an inside chamber of the battery pack casing through the inlet section. The air flows in the gaps formed between the battery cells in the battery pack casing. The inside air is discharged outside through the outlet section of the battery pack casing. That is, after heat-exchange of the air in the battery pack casing, the air is discharged outside from the battery pack through the outlet section. In other words, the heat-exchanged air is not recirculated in the inside chamber of the battery pack casing, and discharged outside through the outlet section of the battery pack casing. Further, a fresh air is introduced into the inside of the battery pack casing. In the structure of the battery pack previously described, the air flowing in the battery pack casing and fresh air introduced into the battery pack casing do not have a uniform temperature distribution (or a uniform temperature variation). Accordingly, a plurality of temperature detection devices and wires is necessary in the battery pack having such a conventional structure in order to detect a correct temperature of the battery cells and transmit detection signals to an outside control unit through the temperature detection wires.
However, in the battery pack having the conventional structure disclosed in the Japanese patent laid open publication No. JP 2007-329047, because the battery cells are cooled by the inside air flowing in the inside of the battery pack casing and the inside air is discharged outside through the outlet section, the temperature detection wires prevent a smooth flowing of the inside air in the battery pack casing. As a result, this provides an adverse influence on the battery cooling characteristics of the battery pack.
For example, when a vehicle such as a hybrid vehicle or an electric vehicle is equipped with a battery pack having a plurality of battery cells, it is necessary to have a plurality of temperature detection devices such as battery temperature thermistors capable of detecting a battery temperature of each of the battery cells, a plurality of temperature detection wires, and a control device such as a battery management unit equipped with a plurality of input ports. This increases the number of components of the battery pack mounted on the vehicle and the total manufacturing cost of the vehicle.